This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. TUT4, or terminal uridylyl transferase 4, is one of a family of RNA-editing enzymes found in trypanosomatids. Although it?s exact role has yet to be identified, it?s basic function, like other TUTases involves the incorporation of UMP into RNA strands that must first be edited prior to translation. Trypanosomatids are responsible for fatal diseases such as African sleeping sickness, Chagas disease, and leishmaniasis. Furthermore, no closely homologous enzymes have been found in humans, making TUTases good potential drug targets. TUT4 is currently the smallest known TUTase and contains all of the conserved functional domains, making it an attractive target for crystallographic investigation with aims such as identifying novel enzyme mechanics and how nucleotide base specificity is achieved. A native data-set has already been collected on a crystal of this enzyme. However, since there are no protein structures available with enough sequence homology, heavy-atom derivatives and are being generated to solve the phase problem. Therefore, a MAD beam line is necessary for further experimentation.